The present invention may be regarded as an extension of U.S. Pat. No. 7,095,678 “Method for seismic imaging in geologically complex formations” to Winbow and Clee, which document is incorporated by reference into the disclosure herein.
The technical problem primarily addressed herein is the class of depth imaging situations where azimuth information at each image point is needed. Such azimuth information should take account of 3D variation of velocity and anisotropy as well as the dip of the target reflectors. Such information is useful in understanding the fracture properties of carbonate reservoirs found, for example, in the Caspian and the Middle East. Such fracture information is important to efficient hydrocarbon exploration of and production from such reservoirs because it is an important influence on the porosity and permeability of petroleum reservoirs. Present ray based imaging methods such as Kirchhoff are computationally efficient but are limited to producing seismic volumes that have constant surface (i.e. source-receiver) azimuth. This is because the maps used in the migration only contain travel times and therefore are unable to direct the output into files depending on reflection angle or reflection point azimuth. Wave equation based methods are more time consuming and expensive than ray based imaging methods. Therefore there is a need for a ray-based method that can obtain azimuthal information at the reflection points. The method should migrate 3D seismic data into common reflection point azimuth seismic volumes using ray based imaging methods, where the azimuths are defined at the image point and are valid for any dip of the target reflector. The method should be applicable for any acquisition geometry whether it is land data, bottom cable data or marine data, provided that the subsurface is not so complex that it requires wave equation methods to form adequate images.